Typically the test that one does to determine exposure is to measure at what density exposure breaks the film threshold. That is normally a measurement of .10 above film base plus fog. That would correspond to an exposure four stops less then meter reading. The corresponding highlight density will depend on the enlarger light source. Typically that is quoted as a Zone VIII value. That would be three stops above meter reading for a uniformly light textureless surface. The value for this is typically valued at 1.10-1.15 for condensor enlargers and 1.20-1.25 for diffusion light sources.

This above is all Zone System parlance. There are other systems and tests to determine exposure but the explanation that I gave is more in line with the question that you posed.